Flange sealing surface generally in the form of the following

Raised face flanges (RF), the convex surface of the flange (M / FM), ring joint face flange (RTJ).
Toxic media, as long as it is not extremely hazardous level, pressure rating less than or equal to 1.6MPa, the flange raised face RF 2.5MPa generally requires the use of the convex surface of the flange. For extreme hazards medium, requires the use of the convex surface of the flange.
Convex surface of the flange is usually used in the German standard and national standard PN4.0 level PN6.4MPa mainly determined by the pressure level, the convex surface of the flange sealing the ordinary convex flange (RF) better, but not easy to replace gasket. The use of the tongue and groove face flange with the convex surface of basically the same.stainless steel hydraulic hose fittings
Ring joint face flange (RTJ) is mainly used in high temperature, high pressure, or both conditions. American Standard flange, commonly used in Class 600Lb (part), 900Lb, 1500Lb, 2500Lb Pressure Level. Commonly used in the German standard flange and GB flange in PNl0.0, PN16.0, PN25.0, PN32.0, PN42.0MPa flange. Gasket with stainless steel ring.
General toxic and harmful media, not recommended a common plane flange and raised face flanges should be used in the convex surface of the flange or better than its sealing performance.hose adapters